The present invention relates to a radiation image storage panel favorably employable in a radiation image recording and reproducing method utilizing stimulated emission. The invention also relates to a process for reading radiation image information stored in the radiation image storage panel.
When a stimulable phosphor is exposed to a radiation such as X-ray, it absorbs and stores a portion of the radiation energy. The stimulable phosphor then emits stimulated emission according to the level of the stored energy when the phosphor is exposed to an electromagnetic wave such as visible light or infrared rays (i.e., stimulating ray).
A radiation image recording and reproducing method utilizing the stimulable phosphor has been widely employed practically. The method employs a radiation image storage panel comprising the stimulable phosphor, and comprises the steps of causing the stimulable phosphor of the storage panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with a stimulating ray such as a laser beam to emit a stimulated emission; and photoelectrically detecting the emitted light to obtain electric signals. The storage panel thus treated is subjected to a step for erasing radiation energy remaining therein, and then stored for the use in the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly used.
The radiation image storage panel (often referred to as stimulable phosphor sheet) has a basic structure comprising a support and a stimulable phosphor layer provided thereon. On the free surface (surface not facing the support) of the phosphor layer, a protective film is generally placed to keep the phosphor layer from chemical deterioration or physical damage.
The stimulable phosphor layer usually comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder.
In U.S. patent application Ser. No. 09/749,623, a modified radiation image recording and reproducing method is described. In the method, a function for absorbing radiation and a function for storing the radiation energy are separated, while a stimulable phosphor used in the known radiation image recording and reproducing method performs both functions. For that purpose, a radiation image storage panel comprising at least a stimulable phosphor (for storage) and a fluorescent screen comprising a fluorescent phosphor which absorbs radiation and emits ultraviolet or visible light are used in combination. The method comprises the steps of exposing the fluorescent screen to a radiation having passed through an object or having radiated from an object and converting the radiation into ultraviolet or visible light by the fluorescent phosphor; having the ultraviolet or visible light absorbed by the stimulable phosphor; sequentially scanning a stimulating ray on the stimulable phosphor of the storage panel to emit a stimulated emission; and photoelectrically detecting the emitted light to obtain electric signals of the radiation image. The radiation image storage panel of the present invention can be employed in the method of U.S. Ser. No. 09/749,623.
A modified process for reading radiation image information in the form of a simulated emission is also proposed so as to shorten the time for reading, to manufacture a small-sized apparatus and to reduce the manufacturing cost. In the proposed process, the radiation image is divided into pixels by a photodetector (such as a two-dimensional solid image pick-up device or a semiconductor line sensor) to obtain a time-dependent series of image signals through an electric circuit. Japanese Patent Publication No. 5-32945 describes an apparatus for a process comprising the steps of exposing a radiation image storage panel to stimulating rays having emitted from a light source (e.g., a fluorescent lamp) through a slit for linearly stimulating the storage panel (i.e., line stimulation), and detecting the stimulated emission having emitted from the storage panel by a line sensor comprising many photoelectric converting elements (i.e., line detection). The line sensor is placed so that it can face the stimulating rays-exposed area of the storage panel.
In the radiation image recording and reproducing method (and the process for reading radiation image information) described above, the obtained image signals can be subjected to various image-processing so that a sufficient amount of image information can be obtained by applying a small dose of radiation. Further, since the radiation image storage panel can be repeatedly used, the method is also advantageous from the viewpoint of conservation of resources and economic efficiency.
It is desired that radiation image storage panels used in these methods have sensitivity as high as possible and to provide an image of as high quality (e.g., high sharpness, high graininess) as possible.
For improving the sensitivity and the image quality, some methods have been already proposed. For example, Japanese Patent Publication No. 7-27078 describes a radiation image information reading apparatus for the process using a radiation image storage panel having a stimulable phosphor layer formed by vapor-accumulating method. The stimulable phosphor layer in the panel is composed of prismatic blocks sectioned with cracks. The stimulating rays are applied on one face of the storage panel, and the stimulated emission emitting from the same surface is detected by a photoelectric converter. Further, Japanese Patent Provisional Publication No. 62-47600 proposes a method in which a stimulable phosphor layer of radiation image storage panel is formed by electron beam-evaporating method (which is a kind of vapor deposition method). In the method, an electron beam generated by an electron gun is applied onto a stimulable phosphor or starting materials thereof (vapor source) to vaporize the source, to scatter and to deposit the vapor on the surface of the support. Thus formed phosphor layer consists of prismatic crystals of the stimulable phosphor. Generally, a phosphor layer formed by vapor deposition method such as electron beam-evaporating method comprises only a stimulable phosphor with no binder, and in the phosphor layer there are cracks among the prismatic crystals of the stimulable phosphor. For this reason, the stimulating rays are efficiently applied to the phosphor and the stimulated emission are also efficiently taken out. Hence, a radiation image of high sharpness can be obtained with high sensitivity.
In the case where the phosphor layer is formed on the support by vapor deposition method such as electron beam-evaporating method, formed prismatic phosphor crystals have growing open ends (top ends not facing to the support) that usually have flat surfaces or various complex surfaces (mixture of flat, concave and convex surfaces). The present inventor has found that, if the end (top) of each prismatic crystal has a flat or concave surface, the stimulated emission is diffused when it comes out from the surface of the phosphor layer, even though the stimulating rays and the stimulated emission are not diffused in the phosphor layer of the prismatic phosphor crystals. In that case, even if photoelectric converters receive the emission through a light-collecting optical system, the emission is so diffused as to lower the light-collecting efficiency. Consequently, the sensitivity and the image quality such as sharpness are impaired.
An object of the present invention is to provide a radiation image storage panel which is improved in sensitivity and collecting efficiency of stimulated emission.
Another object of the invention is to provide a process for reading radiation image information, by which a radiation image of high quality can be rapidly obtained with high sensitivity.
The present invention resides in a radiation image storage panel comprising a support sheet and a phosphor layer formed on a surface of the support sheet by vapor-accumulating method, wherein the phosphor layer comprises prismatic crystals of phosphor aligned in the same direction, and each of the crystals has a convex surface at one end.
Here, xe2x80x9ceach of the crystals has a convex surface at one of the endsxe2x80x9d means that not less than 95% of the prismatic crystals have convex ends.
Preferred embodiments of the radiation image storage panel are as follows.
(1) The radiation image storage panel wherein the phosphor is stimulable phosphor.
(2) The radiation image storage panel, wherein the crystal has a convex surface at the end not facing the surface of the support.
(3) The radiation image storage panel wherein the support is a transparent support, and the crystal has a convex surface at the end facing the surface of the support.
(4) The radiation image storage panel wherein the convex surface is a spherical surface.
(5) The radiation image storage panel wherein the prismatic crystals of phosphor are aligned perpendicularly to the surface of the support.
The invention also resides in a process for preparing a radiation image storage panel, comprising applying electron beams to a stimulable phosphor source to vaporize the phosphor source and depositing the vapor of the phosphor source on the surface of the support, in which the electron beams are gradually reduced in their energy just before the deposition is complete.
The invention further resides in a process for reading radiation image information comprising the steps of:
moving in one direction the radiation image storage panel of claim 3 on which radiation image information is recorded and stored, in relation to a line sensor which comprises plural photoelectric converting elements arranged linearly and which is placed over the convex surfaces of the aligned prismatic phosphors of the storage panel on a line extending from the end of the convex surface of the aligned prismatic crystal in the same direction, under such condition that the line sensor moves on a plane parallel to the storage panel, while the phosphor layer of the storage panel is scanned with stimulating rays in a direction which is different from the direction of the movement of the storage panel and the stimulating rays are applied onto the phosphor layer approximately parallel to the aligning direction of the prismatic phosphor crystals in the phosphor layer;
detecting an emission emitting from the phosphor layer of the storage panel by the line sensor, so as to photoelectrically convert the emission to an electric signal;
detecting an electric signal of the movement of the storage panel in relation to the line sensor; and
comparing the signal of the emission and the signal of the movement of the storage panel to produce a radiation image information in the form of electric signals.
The invention furthermore resides in a process for reading radiation image information, comprising the steps of:
moving in one direction the radiation image storage panel of claim 4 on which radiation image information is recorded and stored, in relation to a line sensor which comprises plural photoelectric converting elements arranged linearly and which is placed below the support of the storage panel on a line extending from the end of the convex surface of the aligned prismatic crystal in the same direction, under such condition that the line sensor moves on a plane parallel to the storage panel, while the phosphor layer of the storage panel is scanned with stimulating rays in a direction which is different from the direction of the movement of the storage panel and the stimulating rays are applied onto the phosphor layer approximately parallel to the aligning direction of the prismatic phosphor crystals in the phosphor layer;
detecting an emission emitting from the phosphor layer of the storage panel by the line sensor, so as to photoelectrically convert the emission to an electric signal;
detecting an electric signal of the movement of the storage panel in relation to the line sensor; and
comparing the signal of the emission and the signal of the movement of the storage panel to produce a radiation image information in the form of electric signals.